Pipette and method of making same



R. L. ELLIOT ETAL 2,398,737

PIPETTE AND METHOD 0F MAKING SAME April 16, 194e.

Filed Feb. 1 9, 1945 E i V Edi var'dMLavo zi,-

Patented Apr. 16,1946

UNITED STATES PATENT OFFICE PIPETTE AND METHOD OF MAKING'SAME Robert L. Elliot, Winchester, Mass., and Edward M. Lavor, Norfolk, Va. e

.application February 19, 1943, Serial No. 476,460

1 Claim.

Our present invention relates to clinical and other pipettes and like glass devices, and to their manufacture. More particularly it aims to provide an improved process for installing mixing elements or beads in the mixing chambers of de,- vices of this class, and correspondingly to improve the resultant structures, as well as to simplify and improve the pipettes in other respects.

In the drawing illustrating by way of example one embodiment of the invention, and represent-- ing the several steps of the novel manufacturing process: I Fig. 1 is an elevation of a mixing or diluting pipette in accordance with the invention;

Figs. 2 to 5 inclusive are a series of enlarged cross-sections of the mixing chamber of the pipette such as that of Fig. 1, showing several succeeding stages in the insertion of the mixing element; 1

' Fig. 6 is an elevational enlargement of a portion of Fig. 1; and

Fig. 7 is a partially diagrammatic view explana tory of prior practice.

Pipettes such as here concerned are employed for diluting in accurate proportions small quantities of liquids. One of their main elds of use is in diluting blood specimens in preparation for obtaining counts of the red or the white cor-V puscles. For such purpose a determined quantity of the blood is diluted in an appropriate liquid agent to destroy one or the other type of the co1"- puscles, the white ones where a count of the red corpuscles is to be made, or the red ones ifvthe white corpuscles are to be counted.

Referring now to Fig. 1, such pipette in general comprises a rod-like glass body or sternl having centrally throughout its length a capillary tubular channel 2 opening at the outer and usually pointed end 3. At the other or inner end of the stem the capillary channel 2 communicates with a mixing chamber 4. Beyond the latter is a relatively short section er neck of the glass tubing,

or specimen and the blood permitted to rise in the capillary tube either to the marking 0.5 or to the marking 1, depending on the diluent. The latter is then sucked into the pipette until it lls the mixing chamber 4 and extends to the graduation marked 101.

The mixing chamber has loose Within it a small mixing element or bead 6 which acts in the manner of a beater or stirring means, to facilitate and speed up the mixing of the blood and the diluent as the pipette is shaken or agitated, manually. or otherwise.

It will be understood that in the usual manufacture of pipettes of this chambered type the manufacture proceeds from a capillary glass tube initially drawn in long lengths and cut as appropriate for the individual pipettes. A cut length of the tubing is heated at the section where the chamber is to be formed and while temporarily plugging the `capillary at the appropriate point a generally globular chamber of the desired size is blown. Such chamber is completely closed except for the small ports at its opposite ends communicating with the central capillary passages of' the stem and neck, such as 2 and 2a ofliig.l 1.

The mixing element or bead 6 obviously must be larger than these capillary ports of the chamber, to retain the bead in the latter and to afford the `desired mixing action.

A chief manufacturing problem, and that with which our invention is largely concerned, has been that of getting the mixing bead into the chamber. Heretofore the procedure for that purpose has involved heating and completely severing the similar to that of the stem l, including a capil' stem and 101 at the neck, in the case of pipettes for red corpuscle counts. These markings correspond to dilutions in the proportions of 101 toH 0.5 and 101 to 1, respectively, as may be required with different diluting agents. Inuse, the pointed end of the pipette is applied to the blood source pipette Vat the mixing chamber, near one or the other of its end portions, as for example at the point indicated by the broken line s-s, Fig. '7.

. This line of severance must be at a point along the chamber, spaced somewhat from one or the other end, such that the resulting aperture is of suicient area to admit the bead. Following insertion of the bead the two completely severed sections of the pipette are heated and rejoined or4 fused together. This method has been slow and expensive, necessitating highly skilled workmanship to obtain satisfactory results.

Referring now more particularly to Figs. 2 to 5, as well as Fig. 1,`it is noted rst that the mixing chamber 4 as illustrated is of symmetrical and generally Velliptical form, as contrasted for example with a usual previous formation substantially as represented'in Fig. 7, wherein the portion of the chamber adjacent the body or stem of the lpipette was oflarger diameter than the 'rest of the chamber. The symmetrical forout of a relatively small sectinf "tliewall ma-l terial, in amanner to form a 'protub'er'ant coni'-v cal nubbin or tip 1. This is readily accomplished by positioning the pipette substantially horizontally and operating at a then under portion of the chamber wall.

Such tip 'l is then severed'as by cutting or breaking it off at its base, as for example in the plane indicated by the dotted line c-c of Fig. 2,

at or close to the union of the tip with the surrounding unmodied portion of .the chamber wall. The material of the tippreferably is s o removed as to present a somewhat beveled or nonradial edge peripherally of the resulting opening 8, Fig. 3, thereby aiordingan annular seat 9 for the subsequent glass insert and closure vmeans to be described.

The pipette is then turned to bring the aperture 8 into an up-facing position, as illustrated for I.example in Fig. 3. A mixing bead 6 isthen inserted `at and dropped through the opening 8 thus made available for the purpose. Such mixing bead 6, which is left entirely free Ywithin the chamber, may be of glass or other material, contrastingly colored or otherwise, and is of any appropriate shape and size such asv not to decrease materially the liquid capacity of the chamber yet to assist in agitating and thorough- 1y commingling the different fluids contained.

The mixing element or bead-6 .as shown by way of exampleconsists of a short piece of a small pencil-like glass rod, thus resembling an ordinary glass bead, perforate or otherwise. Assuming; Fig. Vl of the drawing to be' substantially adapted to serve as a stop against easy rolling of the pipette when it is placed on a flat surface. Since the described closure I0Y thus incorporates a slightly greater mass of material than was removed to form the opening 8, the center of gravity of the chamber 4 is displaced laterally. Hence when the pipette is laid on a fiat surface, such as a laboratory table, the slightly Weighted region of the closure and stop formation I0, H automatically seeks a lowermost position, in con.. tact with the fiat supporting surface. The pipette having turned to such position, the protuberance or bump Il is adequate to restrain further rollingr under ordinary circumstances.

An additional advantage from the process of 'our invention may be had by contrastingly coloring the insert l0 in whole or part, as for example with the color blue, in contrast to the adjacent glass of the chamber wall and also in contrast to the color ofthe mixing bead. The latter generally is white in pipettes for white corpuscle counting and red in those intended for use in preparation for red corpuscle counts. By thus coloring or applying a color design to the plug l0 or the glass material thereof a readily visible marking is provided for identification purposes.

It will be understood that the glass of the pipette as a whole is clear and transparent save for the graduation marks and indicia such as previously mentioned and usually also a relatively narrow longitudinal background or reading strip I2, generally of a White or other enamel. Such strip affords a substantially opaque or semias 'transparent zone against which to observe the a full scale representationk of one size and type of pipette, anl appropriate-mixing-bead may be roughly 1/8 in. long by e in. in diameter, which dimensions may be considerably varied within the conditions above noted. The diameter of the bead-admitting aperture 8 for any particular pipette is made adequate for easy insertion of the given size and shape of bead.

After insertion of the mixing bead 6 the aperture 8 is reclosed and sealed in a manner to restore the chamber 4 to a fluid-tight condition and to confine the bead within it. Under the method of the invention, noting now Figs. 4 and 5, this is accomplished by meansV of a glass` insert or plug I0, which, according to the size of the opening, may range from a globule to the small disk or button of glass as shown. Such closure member or insert I0 is placed in or on the receiving seat 9,y its partly installed position being represented in Fig. 4. Heat is then applied locallyaround the juncture of the insert and the chamber Wall so as to fuse together their constituent glass material.A l

The resultant closure or seal, as best seen in Figs. 5 and 6, conforms in general to the contour of the chamber wall, with the generally circular line of union scarcely discernible. 'I'he insert l0, however, desirablyis of a thickness relative to the chamber wall asa whole and is so shaped` at its outer surface as lto be somewhat protuberant.

content of the fine capillary passage 2, 2a with reference to the graduations and indicia.

While the bead-admitting aperture may be formed at any point circumferentially of the mixing chamber, it. is preferably located at or within the opaque reading strip l2. In this manner the clear area of the chamber wall is retained in its original unmodified and unobscured condition.

Pipettes of the general character here concerned have heretofore usually Ibeen formed at their suction-applying or shorter end with a relatively small chamber-like enlargement such as indicated at M, Fig. '7, tapering outwardly and terminating at about the same diameter or somewhat smaller than the Vcapillary sections of the pipette, but with an end opening of considerably larger diameter than that of the capillary passage. ySuch formation is believed to have been provided as a safety measure, when the technique called for the application of the pipette directly to the users mouth, to suck the diluting liquid in at the opposite, pointed end. The chamber such Yas M was intended as a trap to receive any excess that might accidently be drawn in, rather than to have it enter the users mouth.

But under present practice, a length of rubber or other flexible tubing such as indicated at T. Fig. 1, is installed at the short or neck end of the pipette. The tubing may have a rigid mouthpiece P at its free end. The latter is inserted in the users mouth, which is thus kept at some distance from the pipette itself, thus substantiallyv eliminating the possibility of uid from the pipette entering the persons mouth, or conversely the likelihood of any contaminant from the mouth being received by the content of the pipette. f

'In the .improved pipette of our invention as' here illustrated the .installationv of 'such tubing is facilitated and the structure of the pipette itself materially simplified by a construction for the neck 5 substantially as illustrated in Fig. 1. As there seen the capillary passage 2a of the neck 5 is continued uniformly for substantially the full length of the latter. outer end of the neck the outer cylindrical surface of the latter is provided with a protuberant annular formation, beading or rib I3 concentrically surrounding the end opening of the capillary passage 2a, which may there be slightly enlarged if desired. This rib I3 is relatively shallow and of rounded formation in cross-sectional contour, so that the end of the flexible tubing T, which is of a size to grip snugly about the pipette neck, is nevertheless easily forced onto the latter. The retaining rib I3 then serves to hold it securely against accidental displacement.

It will be understood that our invention, both as to method or product, is not limited to the exemplary steps or embodiment herein illustrated or described, and We set forth its scope in our following claim.

We claim:

At or near the extreme` In the manufacture of glass pipettcs of the clinical type, that method which comprises the steps of forming a closed chamber of selected volume between opposed capillary tubular stems having capillary ports communicating with the chamber, thereafter heating and forming to a projecting tipa single selected area of the mixing chamber wall spaced from the capillary ports, separating the tip at the outersurface of the chamber wall thereby to aperture it for inward passage of a mixing bead, freely passing such mixing bead from outside the chamber wholly through the wall aperture and so as to be loosely contained in the chamber, selecting a disk-like vbody of glass proportioned to seat peripherally at the aperture and of a composition visually contrasting with that of the chamber wall, and externally insetting and fusing such selected glass body at the aperture thereby reclosing it com pletely by glass wall-forming means and identifying the manufacture of the pipette.

ROBERT L. ELLIOT.

EDWARD M. LAVOR. 

